# Nanomechanical Spectroscopy of Ultrathin Silicon Nitride Suspended Membranes

## TL;DR

This study investigates the mechanical properties of ultrathin silicon nitride suspended membranes using AFM-based nanomechanical spectroscopy, revealing higher elastic modulus and reduced stress post-fabrication, with models for elastic modulus and capillary forces.

## Contribution

It provides new measurements of elastic modulus and stress in ultrathin silicon nitride membranes and introduces a mathematical model for normalized elastic modulus and capillary force effects.

## Key findings

- Elastic modulus of suspended membranes is higher than on substrate.
- Net stress decreases after membrane suspension.
- Capillary forces can cause membrane collapse.

## Abstract

Mechanical properties of a nanomechanical resonator have a significant impact on the performance of a resonant Nano-electromechanical system (NEMS) device. Here we study the mechanical properties of suspended membranes fabricated out of low-pressure chemical vapor deposited silicon nitride thin films. Doubly-clamped membranes of silicon nitride with thickness less than 50 nm and length varying from 5 um to 60 um were fabricated. The elastic modulus and stress in the suspended membranes were measured using Atomic Force Microscope (AFM)-based nanomechanical spectroscopy. The elastic modulus of the suspended membranes was found to be significantly higher than those of corresponding thin films on the substrate. A reduction in the net stress after the fabrication of suspended membrane was observed and is explained by estimating the contributions of thermal stress and intrinsic stress. We establish a mathematical model to calculate the normalized elastic modulus of a suspended membrane. Lastly, we study the capillary force-gradient between the SiNx suspended membrane-Si substrate that could collapse the suspended membrane.

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Source: https://tomesphere.com/paper/1903.02289